The present invention relates to a non-contact inspection system for detection and identification of defects, especially light diverting and transparent defects with optical properties, in transparent media. The system is intended to operate on a continuous production line at line speed, for the detection and location of a variety of types of defects, including bubbles, scratches, cracks, inclusions and other defects in a variety of transparent media including flat and curved glass and plastic articles. In particular, the invention is intended to identify the location of the defect within the thickness of the transparent medium, using stereo vision.
In processes for manufacture of transparent media, it is necessary to be able to inspect the transparent media for defects. Such defects may be in the form of scratches, bubbles, chips, blemishes and a wide variety of other defects. However, the mere detection of defects is insufficient in that the manufacturer of the transparent media needs to know whether the defects are insignificant e.g. minor in nature and thus acceptable to the customer, or a major flaw such that the transparent media would not conform to specifications established by the customer.
It is possible to use human visual inspection of transparent media and to identify those articles of transparent media that have defects. In addition, using visual inspection, it is possible to identify the location and possibly the type of defect. However, human visual inspection is not acceptable because of the time and cost involved in conducting a visual inspection, and the limitations of such a method. It would be preferable to be able to conduct the inspection on-line in the production process, at production speeds, so that defects could be rapidly identified and communicated to production personnel and/or the articles of transparent media with the defects could be readily and quickly separated from articles meeting quality specifications in an effective manner.
Methods have been developed for the inspection of sheets of glass using optical techniques that involve use of lasers. While lasers can be very effective in the detection of defects in flat or essentially flat sheets of glass, imaging optics for laser light require a small f-stop i.e. a large aperture and consequently the depth of field is small. This limits the usefulness of laser light, especially in circumstances where the glass or article has curvature. One example of such a curved article is the face plate of a cathode ray tube (CRT), which requires good optical properties. Focusing on the surface of a curved article to detect defects is difficult if the depth of field of the imaging optics is small.
Apparatus and a method have now been found for detection, identification and location of defects, especially light diverting with optical properties, in a transparent medium using stereo vision techniques.
Accordingly, one aspect of the present invention provides apparatus for the detection and measurement of light diverting and transparent defects with optical properties in a transparent medium, comprising:
a) an extended source of illumination:
b) a first optical recording device;
c) a second optical recording device:
d) means to pass said transparent medium between said extended source of illumination and said first and second optical recording devices,
said first and second optical recording devices being disposed to record images at opposed acute angles from a common location on the transparent medium,
said second optical recording device having two sources of laser illumination attached thereto, said sources of laser illumination being directed at said common location in a spaced apart relationship such that laser light scattered by surfaces of the transparent medium is recorded by the first optical recording device.
In a preferred embodiment of the present invention, said first and second optical recording devices are adapted to be moved from a first location to a second location on the transparent medium.
A further aspect of the present invention provides a method for the detection and measurement of light diverting and transparent defects with optical properties in a transparent medium, in apparatus comprising:
a) an extended source of illumination:
b) a first optical recording device;
c) a second optical recording device:
d) means to pass said transparent medium between said extended source of illumination and said first and second optical recording devices,
said first and second optical recording devices being disposed to record images at opposed acute angles from a common location on the transparent medium,
said second optical recording device having two sources of laser illumination attached thereto, said sources of laser illumination being directed at said common location in a spaced apart relationship such that laser light scattered by the transparent medium is recorded by the first optical recording device;
said method comprising passing an article of a transparent medium between said extended source of illumination and said optical recording devices,
illuminating said transparent medium with said extended source of illumination and said laser illumination,
recording images of said transparent medium with each of said optical recording devices, including recording laser illumination scattered by opposed upper and lower surfaces of the transparent medium at said common location, and
determining the location of said defect within the transparent medium.